The coadsorption of oxygen and potassium on Ru(001): Evidence for the formation of K–O compounds

In order to study an adsorption system where bond formation between coadsorbates competes with the adsorbate–metal substrate bond, we have investigated the interaction between oxygen and a potassium monolayer on Ru(001). At low exposures of oxygen (0.4 L), vibrational, photoemission, Auger, and workfunction data indicate the formation of a KO2 species. EELS spectra are characterized by an intense K–O stretch at 240 cm−1 and the absence of Ru–O stretching modes. Auger spectra indicate a K:O stoichiometry of 1:2 and photoemission spectra contain features indicative of O–O bond formation. Subsequent exposure of oxygen results in the adsorption of atomic oxygen with a characteristic Ru–O stretching vibration at 615 cm−1. Annealing of the K–O layer results in the decomposition of KO2 to Kad+Oad, both being bonded more strongly to the metal substrate than the individually adsorbed species and thus indicating through-metal interactions between atomic oxygen and potassium.